Project summary Understanding how infection with the mouse-adapted Lansing isolate of poliovirus type 2 (PV-P2/L) infects wild-type, nontransgenic mice and lead to poliomyelitis has remained an unanswered question for more than 50 years. Remarkably, the ability of this poliovirus strain to infect wild-type mice can be conferred to other virus isolates by the exchange of a 10 amino acid sequence from the VP1 B-C loop of PV-P2/L. Intracerebral infection of wild-type mice with this recombinant virus, PV-414, also leads to the development of paralysis Similarly to PV-P2/L, virus replication of PV-414 is limited to the brain and spinal cord. Neurologic disease associated with virus infection was thought to be due to direct virus killing of motor neurons. To our surprise, we found that these viruses replicate not in neurons but in astrocytes of the brain. In this application, we hypothesize that astrocytes, a major class of central nervous system glia, when virally infected undergo reactive astrogliosis, differentiating to A1 neurotoxic astrocytes. Stimulation of A1 astrocytes is pro- inflammatory and leads to secretion of numerous cytokines that contribute to neuronal and oligodendrocyte death, facilitating development of many neuropathologies. We propose to identify the site of replication within the central nervous system of PV-P2/L and PV-414 using organotypic brain and spinal cord slice cultures derived from wild-type mice. To determine if astrocytes are also sites of PV-414 infection within the spinal cord, organotypic cultures will generated from multiple regions of the spinal cord and infected with PV-414. Indirect immunofluorescence using antibodies against specific cell types will be used to characterize the infected cell. Identification of the soluble neurotoxin(s) secreted by neurotoxic astrocytes during poliovirus infection, and the mechanism by which neuronal death occurs during this response, will provide additional insight into the mechanism of virus induced tissue damage, a more complete understanding of poliovirus pathogenesis, and define the function of reactive astrocytes during viral infection.